Currently, various inspection apparatuses such as a plain X-ray apparatus, CT (Computerized Tomography) and MRI (Magnetic Resonance Imaging) exist in the field of medical treatment, and “diagnostic imaging” that performs diagnosis using images obtained from these inspection apparatuses is actively performed. For example, radiogram interpretation observation is performed in which a physician carries out a radiogram interpretation by comparing a plurality of radiation images that were imaged in time sequence for a disease site of a patient, to thereby grasp the state of progress or state of healing of an affected area and consider the treatment policy.
Monitor diagnosis is also being carried out that displays images output from an imaging apparatus as digital data on a monitor such as a liquid crystal display to perform diagnosis, and this is replacing the conventional method in which film that was imaged is hung on a projector to perform diagnosis. Thus, by handling images as digital data it has become possible to perform various kinds of diagnosis that were not possible with the conventional film, such as changing the gradation and magnifying or reducing an image at the time of diagnosis.
In recent years, with the object of improving the efficiency of radiogram interpretations or enhancing the radiogram interpretation performance with respect to radiogram interpretation observations performed by physicians, a method has been proposed that performs an inter-image operation, beginning with differential processing (subtraction), between images as comparison objects to highlight differences between the images. Highlighting the differences between images makes it possible to prevent errors caused by oversights by the radiogram interpreter.
Although this inter-image operation (subtraction) is generally performed after aligning structures that appear in each image, even when the structures are completely aligned there are cases in which the signal values for the density or brightness or the like of the corresponding structures among both images do not match. Therefore, in some cases artifacts arise in the images obtained by the inter-image operation, due to this signal value difference.
In general, images obtained from an imaging apparatus are not originally acquired for the purpose of an inter-image operation, and each image is independently reproduced as a visible image that is suitable for radiogram interpretation observation. Therefore, each image is optimized in accordance with optimization conditions that are set respectively for each image. In particular, since images that were imaged at different stages in a time series are obtained by performing optimization for each image, uniform optimization is not performed for all of the images. Accordingly, in most cases the signal values for the density or brightness of the structures as described above do not match, and even if an inter-image operation is performed for these kinds of images there is a high possibility that artifacts will arise.
In order to solve the above described problem, a system has been proposed that can carry out a higher precision inter-image operation by performing image processing so as to make each image an image that in suitable for an inter-image operation (see Japanese Patent Laid-Open No. 2001-266147).
However, according to the method described in Japanese Patent Laid-Open No. 2001-266147, there is a problem that a large amount of processing time is required to perform image processing to make images into images suitable for an inter-image operation. There is thus a need for a system that can perform the above described inter-image operation in a shorter time and, furthermore, acquire images with few artifacts.